The telecommunication network infrastructure has been developing and in addition to the traditional data transfer such as web, mail and the like, data transfer of movie or voice and the like is performed on telecommunication networks, and in particular movie data are transferred by multicast. And as a result of the telecommunication network as an infrastructure, the use of telecommunication networks is increasing at home. In the case of home network, not only wired communication but also wireless communication is widely used because of ease of use.
Because of changes in the state of radio wave used in wireless communication, no reliability corresponding to that of wired communication in physical layer can be maintained. Therefore, according to the technology described in “IEEE, AN SI/IEEE Std 802.11, 1999 Edition (R2003),” the mechanism of acknowledging and retransmitting data transfer in the wireless communication set forth in IEEE 802.11 is specified. However, the acknowledgment and retransmission of data transfer in wireless communication are specified only when the wireless communication method is unicast, and they are not specified when the wireless communication method is multicast.
The method of wireless communication is associated with the MAC layer of the transfer data, and the unicast is adopted when the destination address of the MAC layer is the unicast address while the multicast is used when the destination address of the MAC layer is the multicast address. In the multicast used for the broadcast-type distribution of movies, the destination address of the MAC layer is multicast address. Consequently, the data transfer in wireless communication is not acknowledged and retransmitted and as a result their reliability cannot be maintained.
Accordingly, in a multicast communication, in order to maintain reliability by means of the acknowledgment and retransmission of data transfer in wireless communication, JP-A No. 2006-333309 describes a technology of converting a multicast communication into a unicast communication by the transmitter of wireless communication, and reconverting the unicast communication into the multicast communication by the receiver.
And JP-A No. 2007-049382 describes the technology of converting the destination address of the MAC layer of multicast communication from multicast address to unicast address by a transfer apparatus which is a wireless communication apparatus. Since the application that receives a multicast communication processes data in the IP layer, according to the method of converting multicast communication including the IP layer to unicast communication like the technology described in JP-A No. 2007-333309, it is necessary to reconvert to multicast communication. However, according to the method of converting the MAC layer of the multicast communication into the unicast communication and leaving the IP layer in the multicast communication mode like the technology described in JP-A No. 2007-049382, there is no need to reconvert.
And JP-A No. 2004-242063 describes the technology of converting the destination address of the MAC layer of multicast communication from the multicast address to the unicast address irrespective of the wireless communication.